Stationary induction apparatus



April 3, 1962 F. MITTERMAIER STATIONARY INDUCTION APPARATUS Filed Feb. 27, 1957 Msflttornqy.

Z a u United States Patent 3,028,567 STATIONARY INDUCTION APPARATUS Armin F. Mittermaier, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Filed Feb. 27, 1957, Ser. No. 642,795 4 Claims. (Cl. 336-65) This invention relates to stationary induction apparatus, and more particularly to the construction and clamping of the core thereof and to the method of providing such a construction.

Stationary induction apparatus is formed by providing one or more coils on a core formed of magnetic material. One conventional method of making such a core is to stack punched out laminations of sheet magnetic material. The core may be formed of two or more such stacks assembled together to provide a closed magnetic circuit. However, many commercial grades of silicon steel now have better magnetic properties in the direction of rolling than at an angle to the direction of rolling. In other words, when the lines of magnetic flux pass through the steel substantially in the direction of rolling, the core loss is less and the permeability of the steel is higher than when the lines of magnetic flux pass at an angle to the direction of rolling, and these properties are poorest when the lines of magnetic flux are substantially perpendicular to the direction of rolling. With such steels the conventional method of making a core will fail to make the best use of the properties of the steel unless the core is formed of many stacksone for each leg and one for each yokewhich increases markedly the cost of manufacture and assembly.

To obtain an advantage from the phenomenon, a magnetic core may be formed of a wound ribbon of sheet steel having preferred orientation of the grains in the direction of rolling of the strip, that is, in the direction in which the lines of magnetic flux pass through the strip. A core so formed has been found to have high perme ability and low watts loss. The core may preferably be produced by winding a ribbon of magnetic sheet steel fiatwise layer on layer until a core of the desired dimension is formed. Subsequently, if so desired, for convenience,

the core may be cut in two or more places in order to facilitate the assembly of a coil on the core. Cores of this type are sensitive to changes in pressure, particularly after they have been out. If pressure is applied perpena dicular to the face of a joint between two out sections, the Watts loss of the core is held to a practical minimum. The simplest means of providing such pressure is through the use of a resilient band of material which is positioned under tension around the core after the core has been formed.

The relatively unyielding nature of a wound core formed as described above has made it somewhat difiicult to effect the desired tensioning of the band with either ease or economy. Previously, to the applicants best knowledge, the obvious course has been followed of either securing one end of the band and pulling hard onthe other or pulling on both ends of the band and securing them together while the tension is continued. It is most desirable to effect the tensioning of the band about the core more'simply and easily than has heretofore been found possible.

It is therefore an object of this invention to provide an improved core member having a tensioned band positioned around it with the tensioning effect provided by the particular relationship and construction of the ends of the band.

A further object of the invention is to provide an improved method of securing a predetermined constant pres- "ice sure about a core member through the use of a resilient band of material.

In one aspect thereof, the invention provides a method of securing a predetermined constant pressure about a core member which is formed from a ribbon of magnetic sheet steel wound flatwise layer upon layer. The method includes the steps of first positioning a resilient band of metal about the core and positioning a flat rigid member adjacent the ends of the band at a substantial angle to the outer periphery of the core. Then one end of the band is bent over an end and a side of the flat member, and the other end of the band is bent over the other end and the opposite side of the flat member. After this, the assembly of the band ends and the flat member is twisted in a direction to tension the band until the flat member is substantially parallel to the outer periphery of the core. Then the band ends and the flat member are secured in this position, which may be effected by any desired means. The band is thus suitably placed under a predetermined and constant tension, of a magnitude dependent on the angle at which the flat member was maintained and the dimensions of the fiat member.

With this method, the construction is in effect one where one end of the band is bent back inwardly to form a hook, the other end of the band is bent back outwardly to form a hook and the hooks are positioned in tensioned interlocking relation about the flat member.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention, itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing.

In the drawing, FIGURE 1 is a view in perspective, partly broken away, of stationary induction apparatus incorporating the improved construction of this invention;

FIGURES 2 and 3 are fragmentary views in perspective showing steps in the improved method of tensioning the band of metal about the wound core;

FIGURE 4 is an enlarged fragmentary side view in cross section of the improved tensioning construction of this invention;

FIGURE 5 is a fragmentary view in perspective of a possible modification of the invention; and

FIGURE -6 is a fragmentary view in perspective of a second modification of the invention.

Referring now to the embodiment of the invention illustrated in FIGURES 1, 2, 3 and 4, there is shown a stationary induction device 1 having a conventional coil structure 2 formed of suitable magnet wire arranged on one leg 3 of a core member 4 which is made up of two sections 5 and 6. The core 4 is wound from a continuous strip, or ribbon, of magnetic sheet steel; preferably, the ribbon is wound flatwise layer upon layer so as to form a window 7 until the core 4 has been built up to the desired number of layers. In order to facilitate the assembly of coil 2 on leg 3 of core 4, the coil is cut through, as shown at 8 and 9, so that the two sections 5 and 6 can be separated, coil 2 inserted on one of them, and then the two sections brought back together as shown. In order to maintain a constant tension on the core so as to optimize the permeability and minimize the losses therein, particularly if the core has been cut into different sections as shown, a resilient band of metal 10 is positioned about core 4 under tension. Coil 4 may be supported in any desired manner such as, for instance, on a sheet metal base 11 provided with tangs 12 which secure core 4 in position on the base.

Referring now particularly to FIGURE 2, the first step of the improved method of tensioning band 10' will be described. A flat rigid member 13, which is ordinarily of metal and is preferably rectangular as shown and substantially disposed in a single plane, is positioned adjacent to the ends 14 and 15 of band 16* and at a substantial angle to the outer periphery of yoke portion 16 of core '4. As shown, this angle is preferably on the order of 90 in order to obtain the maximum tensioning efiect, as will appear more clearly below. Band is brought around the core 4 until its one end extends past member 13, and is bent outwardly away from the core member, as shown, so as to form a tab 17 which is preferably of approximately the same length as member 13. The other end 14 of band 10 extends straight outwardly, as shown. As can be seen, end 14 of the band is longer than end 15.

Referring now particularly to FIGURE 3, the next step in the tensioning process for band It) is to bend that much of end 14 which extends past end 15 around member 13. When this has been done, end 14 of band 19 extends over end 13 and side 19 of member 13, and tab 17 ex tends over end 2% and the opposite side 21 of member 13. With this construction, the member 13 is confined by the two ends of resilient band 10.

The next step of the process is to grip the assembly of member 13 and band ends 14 and 15, as they are arranged in FIGURE 3, and to twist them relative to core 4 in a direction to tension the band. In the particular construction illustrated, this is efiected by rotating the aforesaid assembly relative to core 4 in a counter-clockwise direction (as seen in FIGURE 3) until member 13 is substantially parallel to the outer periphery of core yoke 16. It can be seen from FIGURE 4 that when member 13 has been moved to this position band end 14 is bent back inwardly relative to core 4 to form a hook and the other band end 15 is bent back outwardly relative to the core to form a second hook, with the hooks being positioned in tensioned interlocking relation about member 13. The tensioning effect is obtained because as member 13 is twisted both ends 14 and 15 are simultaneously and automatically pulled due to their engagement with the member 13 so as to create a tension in band 10. The amount of tension may be determined by the original angle of member 13 relative to core 4 and the dimensions of member 13.

Since ends 14 and 15 are locked around member 13, it is merely necessary to hold member 13 in its position substantially parallel to yoke 16 of core 4 to retain the tension. The desired holding effect may be obtained very easily by any of several arrangements. For instance, as illustrated in FIGURES 1 to 4, a member 22 may be provided having a flat portion 23 which fits on the surface of the periphery of core 4 with suitable tabs 24 extending over the sides of the core so as to secure member 22 against sideways movement. Relatively long tab members 25 extend away from the core at each side of flat portion 23, and when member 13 and band ends 14 and 15 are folded over as shown in FIGURES 1 and 4, they are folded between tab members 25. With the parts in this relative position, it is then merely necessary to fold tab members 25 over the outer surface of band 10, as shown in FIGURE 1, in order to secure the band ends 14 and 15 and member 13 in the position of final assembly.

It will be seen from the foregoing that the novel method provides an improved final construction whereby the tensioned band 10 is put under tension simply and easily and is retained under constant tension without difficulty.

Referring now to FIGURE 5, a second possible con struction of the invention is shown. While the band 10 and member 13 are arranged as before, they are positioned adjacent the outer periphery of that part of the core which is against supporting member 11. In this case, base member 11 is formed with a pair of tabs 26, and after the band ends and member 13 have been twisted to put member 13 parallel to core 4, tabs 26 are bent over to secure member 13 in its position parallel to the core. It can be seen that this is achieved, without requiring an additional piece, simply by forming extra tabs in the base member. Preferably, base member 11 is cut away as shown at 27 so as to preclude the assembly of the ends of band 16 and member 13 from bulging out too much, but it will be understood that if base 11 is suitably formed or if a small bulge is not objectionable, this is not a prerequisite.

Another possible construction for securing member 13 and the ends of band 10 in position is shown in FIGURE 6 where base 11 has a channel 28 formed as shown. Openings 29 are provided opposite each other on each side of the channel and a cotter pin 30 is passed through the openings after the positioning of part 13 parallel to the core 4 as described above. The ends 31 of the cotter pin are then bent over to secure it in place; the position of the pin also secures member 13.

While the invention has been explained by describing a particular embodiment thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In stationary induction apparatus, a core formed from a ribbon of magnetic sheet steel wound flatwise layer upon layer and forming a window; a resilient band of metal positioned about said core under tension for maintaining pressure on said core and having overlapping end portions; a flat rigid member positioned between the ends of said band and substantially parallel to the outer periphery of said core said flat member being disposed substantially in one plane, one end of said band being bent back inwardly to form a hook, the other end of said band being bent back outwardly to form a hook, said hooks being positioned in tensioned interlocking relation about said fiat member; a base member interposed between said band and said core, and means for securing said hooks in said interlocking relation and said flat member parallel to said core.

2. In stationary induction apparatus, a core formed from a ribbon of magnetic sheet steel wound flatwise layer upon layer and cut into separate sections, said sections being positioned in abutting relationship and formmg a window; a resilient band of metal positioned about said core under tension for maintaining a constant pres* sure on the joints of said sections and having overlapping end portions, a flat rigid member positioned bet-ween the ends of said band and substantially parallel to the outer periphery of said core, said flat rigid member being disposed substantially in one plane, one end of said band being bent back inwardly to form a hook, the other end of said band being bent back outwardly to form a hook, said hooks 'being positioned in tensioned interlocking relatron about said fiat member, a base member interposed between said band and said core, and means for securing said hooks in said interlocking relation and said flat member parallel to said core.

3. In stationary induction apparatus, a core formed from a ribbon of magnetic sheet steel wound flatwise layer upon layer and cut into separate sections, said sectrons being positioned in abutting relation and forming a W1I1dOW;.a resilient band of metal positioned about said core under tension for maintaining constant pressure on the joints of said sections and having overlapping end portions, a flat rigid member positioned between the ends of said band and substantially parallel to the outer periphery of said core, said flat rigid member being substantially disposed in one plane, one end of said band being bent back inwardly to form a hook, the other end of said band being bent back outwardly to form a hook, said hooks being positioned in tensioned interlocking relation about said fiat member, and a securing member positioned between the surface of the periphery of said core on the one hand and said flat member and said band on the other hand, said securing member having a tab extending over the outer surface of said band over said fiat member so as to secure said hooks in said interlocking relation and said flat member parallel to said core.

4. In stationary induction apparatus, a core formed from a ribbon of magnetic sheet steel wound fiatwise layer upon layer and cut into separate sections, said sections being positioned in abutting relation and forming a window; a resilient band of metal positioned about said core under tension for maintaining constant pressure on the joints of said sections and having overlapping and portions, a flat rigid member positioned between the ends of said band and substantially parallel to the outer periphery of said core, one end of said band being bent back inwardly to form a hook, the other end of said band being bent back outwardly to form a hook, said hooks being positioned in tensioned interlocking relation about said fiat member, and a base member secured to said core extending on each side of said flat member and said hooks, said base member having openings formed on each side of said flat member and said hooks, and pin means extending through both said openings over said flat member and said hooks and secured within said openings so as to secure said hooks in said interlocking relation and said flat member parallel to said core.

References Cited in the file of this patent UNITED STATES PATENTS 2,218,717 McKee Oct. 22, 1940 2,336,139 Vogel Dec. 7, 1943 2,488,391 Ford NOV. 15, 1949 2,804,600 Duenke Aug. 27, 1957 2,816,337 Gerrard Dec. 17, 1957 FOREIGN PATENTS 746,759 Germany Aug. 23, 1944 

